The King Cab was a decent truck in it day. The only down fall was the stock Ball diff. The Cast metal diff halves would split if you tried to put too much pressure on the diff. Problem with that was you had to tighten the diff down pretty far or the ball diff would slip like mad and burn up. That truck with a gear diff would be excellent.

If you are looking to go fast then sell the King Cab and get yourself a VXL rustler or E-Firestorm Flux and a couple of Lipos. If you just want to relive you childhood then buy some new batteries, a decent 27T stock motor and just do a basic clean up and rebuild of the truck. I personally love old tamiyas but they are not good for being speed machines.